1. Field of the Invention
The present invention relates to a paper delivery mechanism for deliverying sheet by sheet, sheets of paper, notes, and various other sheet-like members in copying machines, printers, facsimiles, scanners, classifiers, presses, note issuing machines, cash dispensers, etc., and to a paper feed roller which is a component of a paper feed device for feeding paper.
2. Description of the Prior Art
As materials for a delivering or feeding roller, various kinds of rubber (natural rubber and synthetic rubber) have been heretofore used. Further, for an application requiring a roller having a higher elasticity, sponges or the like obtained by foaming rubber have been used.
Characteristics required for the materials for the delivering or feeding roller are listed below:
1 There should have a coefficient of friction necessary for imparting a sufficient feeding force to paper. PA1 2 The coefficient of friction is not lowered due to the change in temperature and humidity (low temperature and low humidity), change after passage of year or contaminations such as chemicals (oils and fats), ink, dust, etc. PA1 3 Hardwearing properties are high. PA1 4 When ink adhered to paper is transferred, the other portions of paper are not stained. PA1 5 Elastic modulus can be adjusted in a wide range according to uses.
The performance of existing roller materials with respect to the requirements of the above-described five characteristics is as follows:
With respect to the 1, since the coefficient of friction of rubber is in inverse proportion to hardness, it is necessary to lower the hardness in order to obtain a high coefficent of friction. When the hardness is lowered, the performances in connection with other items 2, 3, 4, and 5 lowered on the other side, which is inconsistent.
Withe respect to the 2, this is a matter of a weak point in terms of properties of rubber itself. At a low temperature and a low humidity, the coefficient of friction is extremely lowered, giving rise to a trouble in feed and an inferiority in delivery. Further, since rubber is a high polymer, the characteristic thereof is unavoidably deteriorated as time passes. The average life of rubber is approximately 2 years. Thus, it is necessary to periodically replace it with new one. Further, since synthetic rubber is an organic substance, there are many rubbers which are low in chemicals-resistance. Thus, when oils and fats are adhered thereto, the coefficient of friction is lowered, and further, the deterioration in characteristic due to denature is accelerated. Further, since the coefficient of friction is .left brkt-top.Sticky.right brkt-bot. in other words, ink, dust or the like tends to be adhered to a roller having a higher coefficient of friction.
With respect to the 3, rubber is low in hardness so that the rubber is shaved by paper and carbon particles (such as pencil, ink, etc.) adhered to paper as time passes to reduce its outside diameter. Replacement of rubber with new one is necessary in case where frequency of use is high.
With respect to the 4, since rubber is high in affinity with oils and fats, ink after printing is adhered to a roller in the press, and the ink is transferred to other portions of paper, resulting in an unavoidable occurrence of stain of paper.
With respect to the 5, the elastic modulus can be adjusted by varying the hardness of rubber, but other characterisitcs are simultaneously changed, making it necessary to keep balance.
In the case where a sponge is used, the above-described problems in connection with the 2, 3, 4 and 5 further becomes prominent.
As described above, materials satisfied with all the requirements described above do not exist, and in addition, the respective characteristics are mutually affected. In the past, therefore, a designer takes the most important characteristic into consideration and at the same time compromises in other aspects to determine various characteristics. Simultaneously, the designer devises a mechanism for covering the characteristics in the inferior portions for use of materials.
In explaining the conventional technique which uses a normal rubber roller, an example will be described herein in detail of a feed mechanism in which a one-side shaft is movable and upper and lower shafts are fixed, out of a double-side driving system used when paper for single slip/double slip are fed.
For the purpose of feeding a sheet of a single slip, one-side drive for imparting a drive force to only one roller out of upper and lower rollers will suffice. However, in order to stably feed a double-slip in which a plurality of sheets are placed one over another, double-side drive for imparting a drive force to the upper and lower rollers is essential. This is because of the fact that in the one-side drive system, paper feed on the side in which no feed force is imparted is delayed, and therefore, a deviation between the upper and lower sheets occurs, causing a trouble in feed.
In considering the paper feed in the feed mechanism, paper obtains a feed force from a feed roller owing to a frictional force. This force F is determined by the product of a coefficient of friction.mu. between paper and the roller and a pinching force P. In order to stably feed paper having a variety of thicknesses, it is necessary to weaken the pinching force P for a thin sheet of paper and gradually increase it as the thickness increases. In the prior art, this has been realized by using a mechanism described hereinbelow.